System for fabrication of indirect dental restorations incorporating optical enhancement

ABSTRACT

The invention provides for a system where a viscous material such as dental composite is heated by various means and is injected into a mold of optically clear self curing material such as silicone or polyvinylsiloxane. This mold is contained in an optically clear glass or other such optically clear retention device that is keyed to allow for the sections of the mold to come together such that there is not rotation or gap between the sections. This will allow that no distortion of the finished product will occur. The outer surface of the retention device is formed in a manner of a focusing lens that will direct the curing light energy directly upon the material contained within the mold. The shape of the retention device can be of any shape from a sphere to any parabolic shape or configuration with the intention of the invention, such that when light energy is in use, it will focus on the mold with the greatest intensity. This will enhance the rate at which the material is cured and for the material to be cured from the outside inward. This will allow for complete curing to the surface and prevent the “oxygen inhibited layer” from forming. By using intermittent light pulses of an appropriate duration and wavelength, the composite shrinks at a prescribed rate.  
     The shrinkage of the material is compensated by feeder tubes filled with composite and fabricated of a material that is impervious to the light energy and thus is not cured when the light is focused on the material being molded. The feeder tubes are under pressure of at least 50-150 lbs./sq. in. This will allow for the material in the tubes to be forced into the main mold as the curing takes place and compensates for the shrinkage that is inherent to the material.  
     The mold and the retention device along with the material within the mold and feeder tubes is heated to a temperature that will maximize the reduction in viscosity for each material used in the process. This heat is maintained prior to being placed within the pressure chamber.  
     Once the initial light curing has taken place, the restoration is removed from the clear mold and is place in an oven under vacuum and heated to a temperature of 200-250 degrees F. for approximately 15 minutes. This process removes any volatile molecules and strengthens the finished restoration.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention pertains generally to pressure molding of fluidmaterials using light energy to cure such materials. It also pertains tomolds fabricated from self curing optically clear materials so thatfluid materials cured with light energy may be used in conjunction withsuch molds.

[0003] 2. Description of the Background Art

[0004] Various types of dental restorative materials that use lightenergy to change from a plastic state to a fused or “cured” state areused in dentistry. These materials may either be placed incrementally inthe tooth and cured in layers or fabricated in the laboratory on a modelmade from an impression taken in the patient's mouth.

[0005] In the first instance where the curing takes place in thepatient's mouth, control becomes a problem. Such control incorporatesability to maintain a dry field, to completely cover all the preparedtooth surface (close the margins), maintain a homogeneous material layerwithout incorporating spaces which have no restorative material, propercontact, contour size, shape, occlusal harmony and depth of cure to namea few. The advantages are that it is quick, has a reasonable successrate and is of moderate expense. It satisfies the patient's desire foran esthetic restoration.

[0006] In the second instance the indirect method which requires a modelmade from an impression allows for complete control over the size,shape, contour, contact, shade and occlusal harmony to name a few. Thedisadvantages are that the model is completely dependant upon anaccurate impression, an accurate stone model (no bubble, cracks etc.),requires more time for fabrication and is much more costly.

[0007] In both instances, shrinkage of the material must be taken intoconsideration. In each case the material does not cure at the surface(an oxygen inhibited layer). In the first instance complete curing bytempering is not possible while in the second instance heat tempering(200-250 degrees F. for 15 minutes) gives the laboratory fabricatedrestoration more strength.

[0008] Laboratory fabricated composite resin inlays and/or crowns areusually assembled in and incremental fashion by placing small amounts ofthe appropriate colored composite in or on the stone die and lightcuring it followed by and additional increment until the properconfiguration is accomplished. Notwithstanding the care with which thematerial may be placed, there is always a difference in the cure andcoverage of the material in the incremental method. In addition clearmodeling resins are used to prevent the instruments from sticking to theresin and ensure one layer sticks to the other. All manufacturers adviseusing only small amounts of this fluid as it has the tendency ofreducing the strength of the cured material. This method is cured fromthe inside out. The light source is unidirectional and as a consequencethe shrinkage is away from the margins and die surface. It requires thata separating material be placed on or in the model such that thepartially cure material may be removed without breaking or mutilatingthe die. It is not desirable to remove the restoration prior tocompletion in this method as it never reseats accurately. Consequentlythe thickness of the restoration cannot be verified prior to curing.Spacer thickness creates a problem when the restoration is to be placedin the mouth and cured. The American Dental Association hasspecifications regarding cement thickness for all types of restorations.The spacer thickness cannot be controlled to a degree such that there isa reproducible specified space between the restoration and the tooth.

[0009] An additional problem with the above method is that to generateocclusal harmony, the finished product must be ground and fitted to thedie. This has the problem of possible fracture or changing of the die.The laboratory technician must be extremely careful in the fabrication.Also if the shade of the restoration has to be changed, the die thenbecomes used again where fracture can be a problem.

[0010] Many patents have been granted whereby the materials used for thefabrication of laboratory restorations are subjected to various methodsto strengthen them. Vacuum, pressure under nitrogen or water, and heatare just some of them. These methods have been used singularly or incombination. In most instances they have met the test of the inventorsintentions.

SUMMARY OF THE INVENTION

[0011] In this invention all of the problems of the previous methodshave been overcome. We use a wax pattern that fills the size, shape,contact, contour and occlusal harmony. This pattern is fabricated from awax that suffers no loss of dimensional shape, is strong, can be removedfrom the die without alteration to check for thickness, the wax can bethickened or thinned very easily and does not adhere to the die suchthat removal from the die might cause the die to be broken. In additionthe wax pattern can be modified such that shades of composites can beadded to cusp tips or colors to fossa by removing wax in certain areasthat will be filled after the initial cure.

[0012] The die spacer is a silicone spray that is blown into or on thedie such that there is no loss of the size and shape of such die as canoccur with other separating materials that are needed in all the othermethods, if they are to be removed easily. Working with wax is and hasbeen a mainstay of the dental laboratory dental profession. To work withit only requires a heated instrument and sharp carving instruments. Itdoes not require grinding with all the dust and debris that goes alongwith such procedures. This invention uses the wax in a liquid form froma dispensing device such as a dropper and is of such nature that most ofthe occlusal harmony is accomplished merely by closing the opposingmodel on the semi-solid wax. This method allows for rapid fabrication,checking for thickness and addition or deletion of material.

[0013] Once the pattern is fabricated, and has feeder tubes attached itis surrounded by an optically pure self curing liquid (silicone orpolyvinylsiloxane) to form a mold within a retention device. Uponcuring, the mold is cut in an appropriate manner. The wax pattern isthen removed and composite is pre heated using a device based onapplication 60/343/081 filing date Oct. 27, 2001 and injected into bothhalves of the mold with the proper color scheme. The feeder tubes whichare fabricated of a material which is impervious to light energy arefilled with appropriate shade of composite, and the entire mold andretention device is heated to a temperature that will take advantage ofthe lowest viscosity of the material within the mold without causing anychemical or setting prior to the curing of the material.

[0014] After the mold and retention device are heated to the appropriatetemperature, the entire mold and retention device is placed in apressure apparatus that pressurizes the heated material to a minimum of50-150 lbs./sq.in. The pressurized apparatus is then placed in a lightcuring device that uses intermittent light energy that cures from thesurface inward. This inward curing method allows for “DirectedShrinkage” such that as the material shrinks toward the surface of themold the pressurized material from the feeder tubes makes up anyshrinkage thus allowing for a precision fit that can be duplicated overand over. This is in direct contrast to the methods where smallincrements are placed as the curing is unidirectional toward the lightthus causing the material to shrink toward the greatest mass and awayfrom the margins.

[0015] Following the curing of the material, it is removed from themold, the sprues are removed and the restoration is placed in atempering oven under vacuum at approx. 200-250 degrees F. for 15minutes. It is then placed on the die to check for fit and occlusalinterferences. With the preceding method any adjustments are minimal.Since the wax pattern has a very smooth surface, the resultingrestoration requires only buffing and no major polishing. There iscomplete curing to the surface without any “oxygen inhibited layer”.Should the shade of the restoration be inadequate, small additions tothe surface can be made without any major grinding and/or polishing. Ifa major color change is indicated, a new restoration can be made withinminutes. An added attraction, is that the lab or dentist can hold ontothe mold and should the restoration fracture or come loose and is lost,a new one can be made without any other new impression and model or waxpattern.

[0016] A major advantage to the above system, is that the system isclear and the operator can see if there are any voids within the mold.While the present materials are very strong, reinforcing materials addmuch more strength to the material. The ideal material is various glassor ceramic fibers. It chemically bonds to the resins and is opticallycompatible with the shades of the material. If the glass or ceramicfibers should come to the surface, they can be polished away. This doesnot in any way create a defect in the restoration as the material doesnot wick and does not stretch. Plazma treated polyethelene or kevlardoes not have a chemical compatibility with the resins of the composite.The present invention allows for any such compatible inserts of anyconfiguration to be inserted with ease. The fact that the restoration iscured in one continuous process allows for the elimination of allstresses and voids.

What is claimed
 1. A method and system for laboratory fabricated dentalrestorations using wax patterns or any other moldable material that mayform a pattern.
 2. A system as in claim 1 where the pattern issurrounded by an optically clear self curing material such as siliconeor polyvinylsiloxane but not limited to such materials.
 3. A system asin claim 2 where the optically clear mold material is contained within aretention device.
 4. A system as in claim 3 where the retention deviceis fabricated of an optically clear material such as glass or plastic,but not limited to such materials, with projections in the matingsurfaces of the device to key the mold material so that the mold andretention device may come together as one unit without any openings atthe interface.
 5. A system in claims 1-5 which incorporates holes withinthe retention device, at the interface of the parts, that will allow forhollow sprues to be attached to a pattern in such a way that the patternis placed equidistant between the upper and lower portions of the keyedretention device.
 6. A system in claims 1-5 where the retention deviceis of a spherical shape such that the light energy is focused at thecenter to allow for greater energy concentration.
 7. A system where theretention device is of any shape that will accommodate patterns of anydimension germane to the intention of the invention.
 8. A system as inall previous claims where the retention device and mold combination ispressurized in a container with an appropriate gas between 50-150lbs./sq. in.
 9. A system as in all previous claims where the pattern isremoved from the mold and is replaced by a light cured compositematerial.
 10. A system described in claim 2 where the mold when removedfrom the retention device is cut in appropriate manner such thatcomposite of various shades may be placed in each half of the voidcontained within the mold as described in the previous claim.
 11. Asystem as described in claim 10 where each half of the mold containingthe uncured composite can be cured in a pressure container as describedin claim
 8. 12. A system in all previous claims where incremental curingin each half prior to mating of the retention device, mold combinationcan take place. In such instance each half of the mold containing thecomposite material and retention device is heated to an appropriatetemperature and placed in an optically clear vessel containing a clearwater soluble liquid such as glycerin, but not limited to glycerin, iscontained within a pressure a pressure vessel and charged with a gas.The pressure upon the liquid will force such composite against theadjoining interfaces of mold and said composite that when the compositeis cured with the appropriate intermittent light source, the materialwill not shrink away from the mold surface.
 13. A system in all previousclaims where strengthening inserts or shade enhancing inserts of anyappropriate material may be placed within the composite contained withinthe mold.
 14. A system in all previous claims where sprues and a spruereservoir are attached to a pattern to allow for proper placement withinthe mold and in addition to form openings in the mold subsequent to theremoval of the pattern to allow for injection of a composite materialinto the void made by the removal of the wax pattern and the sprues andsprue reservoir.
 15. A system as in all previous claims, where theretention device has an opening 180 degrees from the sprue and spruereservoir opening to allow for placement of the clear mold material. 16.A system in all previous claims, where subsequent to the mating of bothhalves of the retention device can be secured with a locking device ofany appropriate means such that the mated parts when secured with alocking device will not separate when pressure is applied to the outsideopenings.
 17. A system as in all previous claims where any insert of anymaterial either in the mold itself or the composite contained within themold takes place either as strengthening material for the compositeitself or as a scaffolding. These material may be ceramics, metalssilicones, polyvinylsiloxane materials and the like but not limited tosuch materials within the intention of the invention as stated inprevious claims. Metals inserts may be of any size and shape includingbut not limited to crown copings, implant abutments, temporary implantabutments and the like.
 18. A system as in all previous claims wherelight energy is focused on any point of the retention device and/or moldcombination such that the light completely surrounds this device fromany direction.
 19. A system where the mold may act as a scaffoldingdevice for the placement of any material by any mechanical means,controlled by any method, such that the placement of any restorativematerial on this scaffold will be used to create or enhance esthetics,strength or function. Such placement can be either incremental or in anamount that completely fills the mold.
 20. A system where any form orradiant energy is focused either on the surface of the mold and/or moldkeeper combination at any distance from the mold and/or mold keepercombination such as to cure any form of composite material.